This invention relates to an image-receiving element for use in photographic and photothermographic film units of the diffusion transfer type. More particularly, the invention relates to an image-receiving element especially adapted for use in diffusion transfer film units wherein an image-receiving element is designed to be separated from a photosensitive element after exposure and processing.
Photographic film units of this type are well known and are often referred to as "peel apart" photographic film units. Various embodiments of peel-apart film units are known and include those wherein images are formed in black and white (reduced silver), and color (image dyes), as described in: E. H. Land, H. G. Rogers, and V. K. Walworth, in J. M. Sturge, ed., Neblette's Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold, New York, 1977, pp. 258-330; and V. K. Walworth and S. H. Mervis, in J. Sturge, V. Walworth, and A. Shepp, eds., Imaging Processes and Materials: Neblette's Eighth Edition, Van Nostrand Reinhold, New York, 1989, pp. 181-225. Additional examples of peel apart film units are described in U.S. Pat. Nos. 2,983,606; 3,345,163; 3,362,819; 3,594,164; and 3,594,165.
In general, diffusion transfer photographic products and processes involve film units having a photosensitive element including a support carrying at least one silver halide emulsion, and an image-receiving element including a support and an image-receiving layer. After photoexposure, the photosensitive element is developed, typically by uniformly distributing an aqueous alkaline processing composition over the photoexposed element, to establish an imagewise distribution of a diffusible image-providing material. The image-providing material, (e.g. image dyes or complexed silver), is selectively transferred, at least in part, by diffusion to the image-receiving layer positioned in a superposed relationship with the developed photosensitive element. The image-receiving layer is capable of mordanting or otherwise fixing the image-providing material and retains the transferred image for viewing. The image is viewed in the image-receiving layer upon separation of the image-receiving element from the photosensitive element after a suitable imbibition period. Black and white transfer images are generally formed by exposing and developing a silver halide emulsion, and subsequently dissolving and transferring silver from unexposed, or less exposed regions, to an image-receiving layer containing silver precipitating agents or nuclei. The transferred silver is reduced to metallic silver in the image-receiving layer, thus forming an image. Color images are generally formed by the imagewise transfer of image dyes from a photosensitive element to an image-receiving layer containing a dye mordant material.
Image-receiving elements particularly adapted for use in peel-apart diffusion transfer film units include an image-receiving layer for retaining the transferred image. This image-receiving layer is typically arranged on a substrate layer of suitable material or a combination of layers arranged on the substrate layer. In one well known photographic embodiment, the image-receiving element comprises a support material (preferably, an opaque support material carrying a light-reflecting layer for the viewing of the desired transfer image thereagainst by reflection); a polymeric acid-reacting (neutralizing) layer adapted to lower the environmental pH of the film unit subsequent to substantial transfer image formation; a spacer or timing layer adapted to slow the diffusion of the alkali of an aqueous alkaline processing composition toward the polymeric neutralizing layer; and an image-receiving layer to receive the transferred photographic image. Such a structure is described, for example, in the aforementioned U.S. Pat. No. 3,362,819 and is illustrated in other patents, including U.S. Pat. Nos. 4,322,489 and 4,547,451.
Photothermographic film products for use in diffusion transfer type processes are also well known in the art. Various embodiments of such film products are known and typically comprise: 1) a photosensitive element including at least one photosensitive silver halide emulsion and a corresponding image providing material (e.g. silver for black and white embodiments, image dyes for color embodiments), and 2) an image-receiving element including an image receiving layer. Typically, the photosensitive element is exposed and subsequently brought in superposed contact with the image-receiving element, wherein the assembly is heated for a predetermined time period. In addition to heating, some applications require a small amount of water to be added to the photosensitive element prior to lamination with the image-receiving element. The application of heat, (and water if used), results in the image-wise diffusion of image materials from the photosensitive element, to the image-receiving element Subsequently, the image-receiving element is separated from the photosensitive element. Various embodiments of photothermographic film units and processes are described in: S. H. Mervis and V. K. Walworth, Kirk-Othmer Encyclopedia of Chemical Technology, 4th. Edition, Volume 6, John Wiley & Sons, Inc. 1993, pp. 1036-1039. Specific examples of such film units are described in U.S. Pat. Nos.: 4,631,251; 4,650,748; 4,656,124; 4,704,345; 4,975,361; and 5,223,387.
In both photographic and photothermographic film units, a strip-coat (also referred to as a "stripping layer" or "release layer"), is commonly positioned between the photosensitive element and the image-receiving element to facilitate the separation of the elements from one another after processing. In photographic applications, strip-coats may additionally serve to prevent processing solution from remaining on the image-receiving element after processing. A specific example of such a strip-coat is provided in U.S. Pat. No. 5,346,800 to Foley et al. which describes a strip-coat comprising a hydrophilic colloid, e.g. gum arabic, and an aluminum salt. Other materials are also known for use in strip-coat layers. For example: U.S. Pat. No. 3,674,482 to R. J. Haberlin discloses a strip-coat made of a methyl acrylate/acrylic acid copolymer. U.S. Pat. No. 3,844,789 to Bates et al. discloses a strip-coat prepared from PVP (polyvinyl pyrrolidone). U.S. Pat. No. 4,954,419 to Shinagawa et al. discloses a multi-layer strip-coat including a first a peeling layer containing a copolymer of at least (i) an ethylenically unsaturated monomer containing at least one hydrocarbon group containing from 7 to 18 carbon atoms and (ii) an ethylenically unsaturated monomer, the homopolymer of which is soluble in water or an aqueous alkaline solution. With regard to the monomers which are described as being soluble in water or aqueous alkaline solutions, acrylic acid and vinyl pyrrolidone are listed. It is further disclosed that these constituents may be used either alone in combination.
Materials used in strip-coats may be crosslinked. For example, U.S. Pat. No. 4,629,677 to Katoh discloses a strip-coat comprising a crosslinked copolymer containing more than 40 mole % of a monomer unit derived from an ethylenically unsaturated carboxylic acid or a salt thereof. A specific copolymer disclosed includes a copolymer of acrylic acid and hydroxyethyl methacrylate, (see formula 7 in column 7).
U.S. Pat. No. 4,871,648 to Bowman et al. discloses a strip-coat comprising a copolymer including: (i) one or more randomly recurring units of N-alkyl or N,N-dialkylacrylamides; and optionally, (ii) one or more randomly recurring units of nonionic alkyl-, hydroxyalkyl- (e.g. 2-hydroxyethyl acrylate), or oxaalkylacrylate or methacrylate monomers, or a carboxylic acid group containing monomer; (e.g. acrylic acid); and optionally, (iii) one or more randomly recurring units of polymerized cross-linking monomers having two or more polymerizable groups.
Some strip-coats may produce a noticeable haze over the image-receiving element upon processing and separation from the photosensitive element. It is known that reducing the thickness of the strip-coat will provide some reduction in haze. Such a reduction in the thickness of the strip coat may provide other benefits as well, e.g. an increase in dye transfer therethrough. However, a drawback to providing progressively thinner strip-coats is a reduced effectiveness in facilitating separation between the photosensitive element and the image-receiving element. Furthermore, in photographic embodiments, processing composition often remains adhered to thinner strip-coats after processing and separation from the photosensitive element, thus detracting from the quality of the resulting image. Thus, it is desired to provide a relatively thin strip-coat with low haze which can still effectively facilitate separation between the photosensitive element and the image-receiving element. Furthermore, it is desired to provide such a strip-coat having desirable gloss properties.